1. Field of the Invention
The present invention relates to techniques for increasing the quality of a three-dimensional image (a three-dimensional stereoscopic image), and relates to techniques that can be applied in a wide range of devices that handle three-dimensional images (three-dimensional video), such as cameras (image capturing apparatuses) that capture three-dimensional images, display apparatuses that display three-dimensional images (three-dimensional video), image processing apparatuses that process three-dimensional images (three-dimensional video), and so on.
2. Description of the Related Art
Three-dimensional image capturing apparatuses that capture three-dimensional images in a state where binocular disparity is present (that is, capture a left eye image and a right eye image) are known; such apparatuses make it possible to reproduce a three-dimensional image in a display apparatus (called a “three-dimensional display apparatus” hereinafter) capable of projecting the three-dimensional image (the left eye image and the right eye image) independently for the left and right eyes, respectively.
In three-dimensional image capturing, a three-dimensional image (a left eye image and a right eye image) obtained in a state in which a high level of disparity is present in a far scene (a subject in the far scene) or a near scene (a subject in the near scene) will result in an image that exceeds the fusion limit for three-dimensional viewing by a person and is thus difficult to appear as three-dimensional, or an image that produces a sense of fatigue in people who are viewing the three-dimensional image (a tiring image). In order to avoid generating such a poor three-dimensional image, there are techniques that obtain favorable three-dimensional images by performing disparity adjustment, stereo base adjustment (called “SB adjustment” hereinafter), and so on, and such techniques are widely used in professional three-dimensional image capturing for movies and the like.
Disparity adjustment is a technique used primarily in the case where a far scene (a subject in the far scene) exceeds the fusion limit, and adjusting the disparity so that the distance to the far scene is compressed in a nonlinear manner brings the far scene (the subject in the far scene) that was difficult to see three-dimensionally nearer, making it possible to obtain a three-dimensional image that is easy to perceive in three dimensions (a three-dimensional image that can easily be seen in three dimensions).
On the other hand, stereo base adjustment reduces the space between two cameras (a camera for capturing a left eye image and a camera for capturing a right eye image) (that is, reduces the stereo base (interaxial distance)), making it possible to reduce the dynamic range of the disparity. For this reason, capturing a three-dimensional image after performing the stereo base adjustment described above makes it possible to obtain a three-dimensional image in which the entire scene, from the far scene (a subject in the far scene) to the near scene (a subject in the near scene), is within a fusional area.
In addition, even in the case where the three-dimensional image is displayed in a display apparatus at a small size, the disparity of the three-dimensional image (that is, between the left eye image and the right eye image) is reduced, and thus the far scene is compressed. Accordingly, in this case, the three-dimensional image displayed in the small-size display apparatus is a three-dimensional image that is easy to view.
Employing the stated image capturing techniques (disparity adjustment, stereo base adjustment) in three-dimensional image capturing makes it possible to capture a three-dimensional image that is sufficiently easy to view (that is, a three-dimensional image that is easily perceptible in three dimensions) when displaying the image in three dimensions in a predetermined display environment (for example, see Japanese Patent H8-9421A).
However, in the aforementioned conventional technique, a three-dimensional image that is easy to view (that is, a three-dimensional image that is easily perceptible in three dimensions) is obtained by taking the fusion limit for three-dimensional viewing into consideration and reducing the desired disparity (that is, by reducing the disparity from its original value so that the subject that is the target of the three-dimensional image capturing falls within the fusional area for three-dimensional viewing), and is therefore not desirable from the standpoint of obtaining a natural sense of three-dimensionality and depth in the three-dimensional image. Accordingly, three-dimensional images using the aforementioned conventional techniques (techniques employing disparity adjustment and stereo base adjustment) have a problem in terms of the quality of the three-dimensional images.
Techniques employing disparity adjustment can obtain three-dimensional images that are easy to view (that is, that are easily perceptible in three dimensions), but because the distance to the far scene is compressed in a nonlinear manner, a phenomenon in which the far scene appears as a flat plane (that is, a phenomenon in which a sense of thickness in subjects in the far scene is reduced and the subjects appear as flattened three-dimensional images) occurs in three-dimensional images on which disparity adjustment has been performed.
Meanwhile, techniques employing SB adjustment have an overall reduced sense of depth in the three-dimensional images that are obtained (that is, the distance from the closest point to the farthest point is reduced), and thus a phenomenon in which the sense of three-dimensionality of individual subjects is reduced occurs.
Accordingly, the three-dimensional images obtained using any of the aforementioned conventional techniques tend to be images having a poor sense of three-dimensionality and depth, and thus have poor quality.
In addition, there are cases where what is known as a “cardboard cutout effect” occurs due to the compression/reduction in the sense of three-dimensionality arising in the case where the aforementioned conventional techniques are used.
The “cardboard cutout effect” is a phenomenon in which, in a three-dimensional image, the thickness of, for example, a primary subject such as a person in the near scene is reduced, and the subject resembles a flat picture drawn on a board.
If this cardboard cutout effect occurs in a primary subject, which is of high importance, there will be an extreme drop in the quality of the three-dimensional image.
However, the cardboard cutout effect does not occur only due to the compression/reduction in the sense of three-dimensionality arising in three-dimensional images due to the disparity adjustment as in the aforementioned conventional techniques. Depending on the image capturing conditions (image capturing state), the cardboard cutout effect can occur even in ideal, undistorted three-dimensional image capturing (image capturing that captures three-dimensional images with no compression/reduction in the sense of three-dimensionality).
Accordingly, the cardboard cutout effect is a visual phenomenon, and all of the causes of the cardboard cutout effect have not necessarily been clarified. However, regardless of the cause of the cardboard cutout effect occurring, the effect always reduces the quality of three-dimensional images.
Having been achieved in light of the aforementioned problems, it is an object of the present invention to realize a three-dimensional image processing apparatus, a three-dimensional image processing method, and a program that restore a sense of three-dimensionality and thickness to a subject and obtain a high-quality three-dimensional image with a low sense of a cardboard cutout effect, regardless of the causes of the cardboard cutout effect.